1. Field of the Invention
The present disclosure relates to electrical contact materials having excellent electrical and mechanical properties, and a method for preparing the same.
2. Description of the Conventional Art
Electrical contact materials are contact elements for electrical conduction, used at a portion contacted when an electric circuit is opened/closed in an electric device such as a circuit breaker or switch. The electrical contact materials are applied to motor switches, switch gears, MCBs, compact motors and lamps, automobiles, electric home appliances, and the like.
The electrical contact materials require physical properties of high melting point, excellent electrical conductivity and thermal conductivity, low contact resistance, excellent welding resistance, high hardness related to abrasion resistance, small deformation of a contact surface, and the like.
The electrical contact materials may be divided into contact materials for low current (1 A or less), contact materials for intermediate current (1 to 600 A), and contact materials for high current (600 A or more). Generally, materials having excellent electrical conductivity are used as the contact materials for low current. Materials having excellent electrical conductivity, high abrasion resistance, high melting point, and the like are used as the contact materials for intermediate current. Materials having high melting point are used as the contact materials for high current.
The electrical contact materials may also divided into tungsten based contact materials, silver-oxide based contact materials, and precious metal based contact materials. Contact materials generally used among these contact materials are silver-cadmium oxide (Ag—CdO) based contact materials.
Silver (Ag) has very excellent electrical conductivity and thermal conductivity, low contact resistance, and high corrosion resistance. Thus, the Ag is frequently used as a base material of electrical contacts. However, the Ag has weak abrasion resistance and impact resistance, and is expensive. Accordingly, when the Ag is used as an electrical contact material, the electrical contact material occupies about 30 to 60% of switch fabrication cost.
In order to solve this problem, an alloy of Ag and cadmium oxide (CdO) or an alloy of Ag and nickel (Ni) is used. Particularly, an Ag—CdO alloy is widely used. The Ag—CdO alloy has excellent welding resistance and attrition resistance and has relatively small temperature increasing rate in opening/closing of an electrical contact, and low contact resistance. Thus, the Ag—CdO alloy has stable thermal and electrical properties. Particularly, the Ag—CdO alloy is widely used as an electrical contact material. However, in Ag—CdO based contact materials, as oxidation progresses from the surface of the material to the interior of the material, oxide particles are coarsened, and an oxidation sparse layer is formed. Therefore, the hardness of the contact material is reduced, and the abrasion resistance of the contact material is decreased, thereby causing a trouble. CdO is a material having strong toxicity and has a problem of environmental pollution. The Ag increases the entire cost of the electrical contact material as the price of the Ag increases. Accordingly, it is possible to develop an electrical contact material capable of substituting for the Ag—CdO contact material.
Recently, an electrical contact material prepared by adding a carbon based compound to a metal has been proposed in order to improve abrasion resistance, electrical property and the like of the electrical contact material. For example, Chinese Patents Nos. 102324335, 001624175 and 001256450 have disclosed electrical contact materials including Ag powder and carbon nano tubes (CNTs). The electrical contact materials described in these documents include CNTs, thereby improving electrical characteristics of contact points. However, the electrical contact materials still have high contents of silver (Ag). Therefore, preparation cost is high, preparation processes are complicated, and the like.